1. Field of the Invention
This invention relates to a process for the hydroformylation of olefinic compounds.
2. Description of the Prior Art
One known hydroformylation reaction comprises reacting olefins with a mixed hydrogen/carbon monoxide gas in an organic solvent in the presence of a rhodium catalyst to produce aldehydes with one more carbon atom. This reaction has found industrial use in the production of butyraldehydes from propylene and propionaldehyde from ethylene, for instance. In commercially practicing this hydroformylation reaction, the most serious problem is maintaining the life of the rhodium catalyst because the rhodium catalyst is very expensive.
A number of research investigations have been made for maintaining the catalytic activity of rhodium catalyst in the hydroformylation of olefins. Heretofore, it has been assumed that thermal degradation of the rhodium catalyst is one of the main causes of the activity decrease. Therefore, in order to maintain the catalytic activity, it was necessary to conduct the hydroformylation of ethylene or propylene under very strictly controlled reaction conditions, especially at an adequate reaction temperature and under well selected reaction pressure.
The maintenance of the catalytic activity by the strict adjustment of the reaction conditions is practically applicable only to the hydroformylation of lower boiling olefins such as ethylene and propylene where the reaction products have relatively lower boiling points. In the hydroformylation of these olefins, higher temperature is not required because of ease of distilling off the reaction products from the reaction mixture. On the other hand, in the hydroformylation of olefins where the reaction products are higher boiling aldehydes (e.g. olefins having 5 or more carbon atoms and substituted olefins) it is generally desirable from an industrial viewpoint that the reaction products be separated from the reaction mixture by distillation. During the distillation, however, a part of the rhodium catalyst tends to thermally decompose in the distillation vessel and the resulting metallic rhodium adheres to local portions of the vessel wall. Such metallic rhodium formation not only makes recycling or reuse of the catalyst difficult, but it also necessitates regeneration under severe reaction conditions (high temperature and pressure). For these reasons, the rhodium catalyzed hydroformylation of such olefins under mild reaction conditions has never been practiced commercially.